1. Technical Field
The present invention relates to light-emitting devices for illumination or the like, using a semiconductor light-emitting element.
2. Background Art
Incandescent light bulbs, fluorescent lamps and high-pressure discharge lamps have been used conventionally as light sources for lighting fixtures or billboards. Research into light sources using semiconductor light emitting elements, such as LEDs, as new light sources replacing such conventional light sources, is advancing. These light sources using semiconductor light-emitting elements have the advantage that their lifetime is longer than that of conventional light sources, and they have raised high expectations as illumination light sources of the next generation.
Now, it is easy to observe the lifetime of conventional light sources. For example, when an incandescent light bulb has reached its lifetime, its filaments will break and it will no longer emit light, and what is more, when the light bulb is removed and shaken, the broken filaments will make a rattling noise, so that its lifetime can be clearly established. Moreover, in the case of fluorescent lamps, there will be a darkening near the electrodes due to the adherence of mercury, as well as flickering and lower brightness, so that also in this case it is easy to determine the lifetime.
On the other hand, even though semiconductor light-emitting elements, such as LEDs, have a much longer lifetime than incandescent light bulbs or fluorescent lamps, when they finally reach their lifetime and should be replaced, their characteristics, such as their emitted light amount, deteriorate only gradually, so that it is more difficult to observe their lifetime than that of incandescent light bulbs or fluorescent lamps. Accordingly, particular efforts are necessary to establish that the lifetime of the semiconductor light-emitting elements has come or is about to come.
Moreover, when a semiconductor light-emitting element, such as an LED, is used as an illumination light source, a plurality of semiconductor light-emitting elements are used, and it is necessary to consider differences in the individual lifetimes of the individual semiconductor light-emitting elements caused by differences in their solid-state characteristics.
The following is an explanation of devices described in JP 2002-304904A (referred to as Patent Document 1 below) and JP 2006-236636A (referred to as Patent Document 2 below), in which semiconductor light-emitting elements, such as LEDs, are used as illumination light sources.
The device of Patent Document 1 is configured as shown in FIGS. 11A and 11B. It comprises an LED power supply portion (not shown in the figures) that converts alternating current from a commercial power source into a low DC voltage of a predetermined level by down-stepping, rectifying and smoothing, and outputs this voltage, a main body 111, a fixture shell 112, an LED unit 113, and a lens body 114, for example. A plurality of light-emitting diodes (LEDs) are mounted on the LED unit 113. Lenses 114d that are positioned to the front side of the respective LEDs are arranged on the lens body 114. The LED unit 113 and the lens body 114 are stored removably in the main body 111 and the fixture shell 112, and exchange of the LED unit 113 is possible.
However, Patent Document 1 does not describe a method for determining when the lifetime of the LED unit has come, and states merely that the lifetime of the illumination device can be extended by exchanging the LED unit. Moreover, even though a plurality of LEDs are mounted on the LED unit, no consideration is given to differences among the lifetimes of the individual. LEDs.
The device of Patent Document 2 is configured as shown in FIGS. 12A and 12B. Here, the lighting fixture 121 includes a plurality of LED packages 122 serving as a light source. When the lighting fixture 121 approaches its predetermined lifetime, then the LED package 122 repeatedly lights up, and this lighting state of the LED package 122 is different from the ordinary lighting state, thereby announcing that its lifetime has come. The change in the lighting state of the LED package 122 can be easily and reliably perceived by a user of the lighting device 121.
More specifically, the driving power source (lighting device) includes a lighting circuit for letting the plurality of LED packages 122 light up, a control circuit that can control the lighting of each LED package 122 individually, a determination means for detecting a physical change that correlates with the predetermined lifetime of the lighting fixture 121 including the lifetime of the driving power source, and determining that the lifetime has come based on this, and a notification means for notifying that the lifetime is coming when the determination means has determined that the lifetime is coming.
The determination means detects for example characteristic values (electrostatic capacitance of an aluminum electrolytic capacitor, leak-current of a diode) of an electronic component within the power source for driving (light-emitting device) or the total lighting time of the LED packages 122, and determines that the lifetime is coming when these values exceed predetermined values.
When the determination means determines that the lifetime is coming, the notification means repeatedly turns the LED packages 122 on and off, and by changing the lighting state of the LED packages 122 with respect to the ordinary lighting state, the user can be notified of the fact that the lifetime of the lighting fixture 121 has come.
In Patent Document 2, the total lighting time of each LED package 122 is detected, so that the lifetime of each LED package 122 is detected and notified. However, it is necessary to provide a control means, a determination means and a notification means, so that the costs of the device become high.
Furthermore, the lifetime of the illumination device is taken as a precondition, and even though the total lighting time of each LED package 122 is detected, no consideration is given to differences in the lifetimes of the individual LED packages 122 caused by differences in the individual characteristics of the light sources.